1. Field of the Invention
The present invention relates to a surface-mounted type antenna incorporated in a communication device such as a portable telephone, and to a method for adjusting and setting the dual-resonance frequency thereof. The present invention further relates to a communication device including the surface-mounted type antenna.
2. Description of the Related Art
FIG. 17 shows an example of a surface-mounted type antenna. The surface-mounted type antenna 1 shown in FIG. 17 is formed by juxtaposing a power supplied first radiation electrode 3 and a second radiation electrode 4 to which power is not directly supplied on a dielectric substrate 2 having a rectangular parallelepiped shape, with a space (slit) S therebetween. One end side of the first radiation electrode 3 is connected to a power supply portion (power supply terminal) 5, and the other end side thereof constitutes an open end 3a. One end side of the second radiation electrode 4 is connected to a short-circuit portion (ground short-circuit terminal) 6, and the other end side thereof constitutes an open end 4a. 
By connecting the power supply portion 5 to a signal supply source 7 and directly supplying a signal from the signal supply source 7 to the first radiation electrode 3 via the power supply portion 5, and by supplying the signal which has been supplied to the first radiation electrode 3 to the second radiation electrode 4 by an electromagnetic coupling, the first radiation electrode 3 and the second radiation electrode 4 each resonate, thereby performing an antenna operation (operation of signal transmission/reception).
In a surface-mounted type antenna 1 as shown in FIG. 17, by bringing the resonance frequencies of the first radiation electrode 3 and the second radiation electrode 4 close to each other and by causing the resonance waves of the first radiation electrode 3 and the second radiation electrode 4 to create a dual resonance, a widening of the frequency band of signal transmission/reception can be achieved.
A surface-mounted type antenna 1 as described above is required to be miniaturized. In order to achieve the miniaturization thereof, the spacing between the first radiation electrode 3 and the second radiation electrode 4 is narrowed as an inevitable consequence. As a result, the electromagnetic coupling between the first radiation electrode 3 and the second radiation electrode 4 strengthens. This makes it difficult to stably achieve a desired dual-resonance state which allows a required antenna characteristic condition such as the widening of the frequency band to obtained. In order to solve this problem and to stably achieve a desired dual-resonance state, it is necessary to control the electromagnetic coupling between the first radiation electrode 3 and the second radiation electrode 4.
In the surface-mounted type antenna 1 shown in FIG. 17, by adjusting the width of the uniform-width space S between the first radiation electrode 3 and the second radiation electrode 4, the electromagnetic coupling between the first radiation electrode 3 and the second radiation electrode 4 is controlled. However, the control of the electromagnetic coupling using the uniform-width space S is very difficult to execute, and provides a limited degree of flexibility in the design.
The present invention has been made to solve the above-described problem, and aims to provide a surface-mounted type antenna which allows the miniaturization thereof and which is capable of easily meeting a required antenna characteristic condition, and to provide a method for adjusting and setting the dual resonance thereof, as well as a communication device including the surface-mounted type antenna.
In order to achieve the above-described object, the present invention, in a first aspect, provides a method for adjusting and setting the dual-resonance frequency of a surface-mounted type antenna which includes a dielectric substrate, a first radiation electrode to which power is supplied being formed on the top surface opposed to the mounting bottom-surface of the dielectric substrate, and a second radiation electrode which is juxtaposed with the first radiation electrode on the dielectric substrate with a space therebetween. This method comprises arranging the first radiation electrode and the second radiation electrode so that the strong electric-field regions of the first radiation electrode and the second radiation electrode wherein the electric fields of these radiation electrodes are each the strongest, are adjacent to each other, and so that the-strong electric-field regions of these radiation electrodes thereby come into an electric-field coupling, simultaneously arranging the first radiation electrode and the second radiation electrode so that the high current regions of the first radiation electrode and the second radiation electrode wherein the currents of these radiation electrodes are each highest, are adjacent to each other, and so that the high current regions of these radiation electrodes thereby come into a magnetic-field coupling, variably adjusting each of the quantity of the electric-field coupling between the strong electric-field regions of the first radiation electrode and the second radiation electrode, and the quantity of the magnetic-field coupling between the high current regions of the first radiation electrode and the second radiation electrode, and setting the reflection loss of the dual resonance of the first radiation electrode and the second radiation electrode to a low value not higher than a predetermined value within the range of the set frequency, by adjusting both the quantities of the electric-field coupling and the magnetic-field coupling.
In the method for adjusting and setting the dual-resonance frequency of a surface-mounted type antenna in accordance with the first aspect of the present invention, preferably, the quantity of the electric-field coupling between the strong electric-field regions of the first radiation electrode and the second radiation electrode is variably adjusted, by making variable the spacing between the strong electric-field regions of the first radiation electrode and the second radiation electrode.
Also, in this method in accordance with the first aspect, it is preferable that the first radiation electrode be provided with a capacitance between the open end thereof which is the strong electric-field region thereof on one end side thereof and ground, that a power supply terminal or a ground short-circuit terminal be connected to the high current region thereof on the other end side thereof, while the second radiation electrode be provided with a capacitance between the open end thereof which is the strong electric-field region thereof on one end side thereof and ground, that a ground short-circuit terminal be connected to the high current region thereof on the other end side thereof, and the quantity of the electric-field coupling between the strong electric-field regions of the first radiation electrode and the second radiation electrode be relatively variably adjusted, by variably adjusting the capacitance between the open end of the first radiation electrode and ground, and the capacitance between the open end of the second radiation electrode and ground.
Furthermore, in the method in accordance with the first aspect, it is preferable that the dielectric substrate be formed as a rectangular parallelepiped, and that the capacitive coupling portion between the open end of the strong electric-field region of the first radiation electrode and ground thereof and the capacitive coupling portion between the open end of the strong electric-field region of the second radiation electrode and ground thereof be each formed on mutually different surfaces of the dielectric substrate.
Moreover, in the method in accordance with the first aspect, preferably, the quantity of the magnetic-field coupling between the high current regions of the first radiation electrode and the second radiation electrode is variably adjusted, by making variable the spacing between the high current regions of these radiation electrodes.
Also, in the method in accordance with the first aspect, it is preferable that a conductive pattern be formed which is branched off from the power supply terminal or the ground short-circuit terminal of the first radiation electrode, and which is connected to ground, that a pattern for an inductance component addition be interposed in this conductive pattern, that a current path be formed which leads from the high current region of the first radiation electrode to the high current region of the second radiation electrode via the conductive pattern, ground, and the ground short-circuit terminal of the second radiation electrode, and that the quantity of the magnetic-field coupling between the high current regions of the first radiation electrode and the second radiation electrode be equivalently variably adjusted, by making variable the magnitude of the inductance component of the pattern for inductance component addition.
Furthermore, in the method in accordance with the first aspect, it is preferable that the power supply terminal or the ground short-circuit terminal of the first radiation electrode and the ground short-circuit terminal of the second radiation electrode be juxtaposed with a spacing therebetween, that the power supply terminal or the ground short-circuit terminal of the first radiation electrode, and the ground short-circuit terminal of the second radiation electrode be short-circuited, by utilizing the pattern for inductance component addition, and that the quantity of the magnetic-field coupling between the high current regions of the first radiation electrode and the second radiation electrode be equivalently variably adjusted, by making variable the magnitude of the inductance component of the pattern for inductance component addition.
Moreover, in the method in accordance with the first aspect, preferably, the pattern for inductance component addition is made to also perform the function of an electrode pattern which constitutes a matching circuit.
In accordance with a second aspect of the present invention, there is provided a surface-mounted type antenna comprising a dielectric substrate, a first radiation electrode to which power is applied formed on the surface of the dielectric substrate, and a second radiation electrode which is disposed adjacent to the first radiation electrode on the dielectric substrate with a spacing therebetween. In this surface-mounted type antenna, the strong electric-field regions of the first radiation electrode and the second radiation electrode wherein each of the electric fields of these radiation electrodes is the strongest, are disposed adjacent to each other with a spacing therebetween, the high current regions of the first radiation electrode and the second radiation electrode wherein each of the currents of these radiation electrodes is the highest, are disposed adjacent to each other with a spacing therebetween, and the space between the first radiation electrode and the second radiation electrode diverges from the high current region side to the strong electric-field region side.
Furthermore, in this method in accordance with the second aspect, preferably, a power supply terminal or a ground short-circuit terminal is connected to the high current region of the first radiation electrode, a ground short-circuit terminal is connected to the high current region of the second radiation electrode, the power supply terminal or the ground short-circuit terminal of the first radiation electrode and the ground short-circuit terminal of the second radiation electrode are juxtaposed with a spacing therebetween. It is further preferable that a pattern for inductance component addition which short-circuits the power supply terminal or the ground short-circuit terminal of the power supply radiation electrode and the ground short-circuit terminal of the second radiation electrode, be formed, that the magnitude of the inductance component of the pattern for inductance component addition be set to a value such as to allow the return loss characteristics in the dual resonance of the first radiation electrode and the second radiation electrode to be obtained, the return loss characteristics meeting a predetermined antenna characteristic condition, and that the resonance frequency of the first radiation electrode is lower than that of the second radiation electrode, in the frequency band of dual resonance.
The present invention provides, in a third aspect, a communication device equipped with a surface-mounted type antenna produced by adjusting and setting the dual-resonance frequency using a method for adjusting and setting the dual-resonance frequency of a surface-mounted type antenna, in accordance with the first aspect, or a communication device equipped with a surface-mounted type antenna in accordance with the second aspect.
In the present invention having the above-described features, the first radiation electrode and the second radiation electrode are arranged so that the strong electric-field regions of the first radiation electrode and the second radiation electrode are disposed adjacent to each other with a spacing therebetween, and are simultaneously arranged so that the high current regions of the first radiation electrode and the second radiation electrode are disposed adjacent to each other with a spacing therebetween.
Meanwhile, the present inventors discovered, during our research and development carried out on the surface-mounted type antenna, that the quantity of the electric-field coupling between the strong electric-field regions of the first radiation electrode and the second radiation electrode, and the quantity of the magnetic-field coupling between the high current regions of these radiation electrodes must both be in conditions suited for dual resonance, in order to achieve a dual-resonance state of the first radiation electrode and the second radiation electrode, the dual-resonance condition allowing an improvement in the antenna characteristics, such as the widening of the frequency band.
In the present invention, as described above, when disposing the strong electric-field regions of the first radiation electrode and the second radiation electrode so as to be adjacent to each other with a spacing therebetween, simultaneously disposing the high current regions of these radiation electrodes so as to be adjacent to each other with a spacing therebetween, and thereupon adjusting and setting the surface-mounted type antenna, each of the quantity of the electric-field coupling between the strong electric-field regions and the quantity of the magnetic-field coupling between the high current regions is variably adjusted, and both the quantities of the electric-field coupling and the magnetic-field coupling are set to conditions which allow return loss (reflection loss) characteristics in the dual resonance of the first radiation electrode and the second radiation electrode to be achieved, the return loss characteristics meeting a predetermined antenna characteristic condition such as the widening of the frequency band. In other words, the reflection loss in the dual resonance of the first radiation electrode and the second radiation electrode are set to a low value not higher than a predetermined value within the range of the set frequency. This allows a surface-mounted type antenna having required antenna characteristics to be obtained easily and in a short time.
The above and other objects, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.